1. Technical Field of the Invention
The present invention relates to an information reproduction apparatus and an information reproduction method for reading out an information material having a plurality of clips and reproducing the clips of the information material consecutively.
2. Prior Art
In recent years, the techniques of compression-coding image information and audio information with minimum deterioration and then decoding the compressed-coded information material with a reproducing means have been developed. For example, the MPEG (Motion Picture Experts Group) system standard has been proposed as a scheme for compression-coding and then decoding (expanding) image information and audio information. An audio-video material or the like that has been compressed and multiplexed according to the MPEG system standard consists of a plurality of clips as shown in FIG. 12. Each clip consists of a plurality of clusters, four clusters in the example of FIG. 12. A "cluster" is a unit that is an integral multiple of a unit (for instance, 512 bytes) that is formed on a hard disk (HDD) and generally called a sector. The example of FIG. 12 shows two clips, i.e., a certain clip CP2 and a preceding clip CP1.
In the conventional example of FIG. 12, an information material (MPEG stream) 2 having clips CP1, CP2, etc. is recorded on a hard disk (HDD) 1. The information material 2 recorded on the hard disk 1 is to be decoded by a decoder. However, direct access to the information material 2 cannot be effected between the hard disk 1 and the decoder 2. This is because the MPEG stream is recorded on the hard disk 1 so as to be divided into certain units (for example, 4-byte units; hereinafter referred to as cells 1a) and a DMA buffer 3 needs to be used as a buffer for absorbing a size difference between the cell 1a of the hard disk 1 and the cluster CT. That is, in accessing the hard disk 1, the information material 2 needs to be temporarily stored in a buffer 3A or a buffer 3B.
To decode the clusters of the clips CP1 and CP2, for instance, by sending those to decoders 4a and 4b consecutively, a switcher 5 is used as shown in FIG. 12. The first cluster CT1 of the preceding clip CP1 is stored in the buffer 3A and reproduced by a decoder 4a, and the next cluster CT2 is stored in the buffer 3B and decoded by the decoder 4b. The switcher 5 sequentially outputs the clusters CT as a video signal, an audio signal, or the like by switching between the decoders 4a and 4b. As the switcher 5 switches between the decoders 4a and 4b, the clusters CT of the preceding clip CP1 and the clusters CT of the (ensuing) clip CP2 are reproduced consecutively.
However, the above method requires two channels, i.e., a channel CH1 consisting of one buffer 3A and one decoder 4a and a channel CH2 consisting of another set, i.e., the buffer 3B and the decoder 4b. That is, the decoders 4a and 4b of two channels need to be prepared.
There may be conceived a somewhat improved scheme in which a decoder of one channel is prepared and the transfer of the information material 2 from the hard disk 1 is given the ability of two channels. However, in either scheme, the transfer ability resources of two channels are necessarily required for the reproduction of the information material 2 on the hard disk of one channel, resulting in a cost increase.
In view of the above, there has been proposed a scheme for consecutively reproducing a plurality of clips CP1 and CP2 as shown in FIG. 12 by using resources of less than two channels. This scheme is disclosed in Japanese Unexamined Patent Publication No. Hei. 8-289255. The technique disclosed in this publication employs a scheme in which in a state that there exist a certain clip CP2 and the preceding clip CP1 as shown in FIG. 12, their sizes are adjusted so as to be equal to an integral multiple of the cluster size.
For example, where there exists invalid data DD (called dust data) as at least part of the fourth, i.e., last, cluster CT4 of the clip CP1, the following problem arises. For example, when the decoder 4b decodes the last cluster CT4 including the invalid data DD coming from the buffer 3B, only effective data t excluding the invalid data DD is actually readout. If the time necessary to readout the effective data t is, for instance, 0.1 second, an operation of sending the cluster CT4 of the clip CP1 from the buffer 3B to the decoder 4b is performed for 0.1 second. At the same time that the cluster CT4 is being read from the buffer 3B, an operation of reading out the head cluster CT1 of the clip CP2 from the hard disk 1 and supplying it to the buffer 3A is performed. At this time, the time required for reading out the last cluster CT4 and supplying it to the decoder 4b is equal to the 0.1 second that it takes to readout the effective data t and supply it to the decoder 4b, and hence information, corresponding to only 0.1 second, of the head cluster CT1 of the clip CP2 can actually be readout. Therefore, if the time necessary to readout the head cluster CT1 of the clip CP2 and supply it to the buffer 3A is 1 second, only part of the information material 2, corresponding to only 0.1 second, can be readout from the hard disk 1 and supplied to the buffer 3A.
To avoid the above inconvenience, a special, dedicated encoder is necessary which codes a certain clip CP2 and the preceding clip CP1 so as to produce data having completely the same size even if there exists invalid data DD.